Gemistocytic astrocytoma, light micrograph. Gemistocytic astrocytoma is a燱HO Grade II astrocytoma with a poorer prognosis爐han other WHO grade-matched tumours. They show a higher rate of爌rogression to glioblastoma燼nd some authors suggest they should be considered WHO Grade III tumours. The histologic hallmark is the presence of爂emistocytes? large tumour cells with abundant dense eosinophilic cytoplasm displacing the nucleus eccentrically. Gemistocytes are frequently found in other fibrillary astrocytomas and oligodendrogliomas. Some authors require at爈east 20% of tumour cells to be gemistocytic燽efore using the designation of gemistocytic astrocytoma. This tumour appears to be composed of an almost pure population of gemistocytic cells.